CN110903422B - Polymerization inhibitor and preparation method and application thereof - Google Patents
Polymerization inhibitor and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a polymerization inhibitor and a preparation method and application thereof. The polymerization inhibitor comprises a compound with the following structural general formula
And/or
Wherein R is1Is H or methyl, R2Is methyl or ethyl, m is 20 to 40, preferably 25 to 35, and 1. ltoreq. x. ltoreq.m. The polymerization inhibitor is a high-molecular homogeneous phase load type, and is suitable for a high-boiling point (methyl) acrylate reaction system. The polymerization inhibitor can effectively prevent the polymerization of raw materials and products, remarkably reduces the entrainment effect of the products on the polymerization inhibitor in the separation process, and ensures the purity of the products. Meets the downstream use requirements, thereby having good application prospect.
Description
Technical Field
The invention relates to the field of polymerization inhibition, in particular to a high-molecular homogeneous phase supported polymerization inhibitor and application thereof in preparation of (methyl) acrylic ester.
Background
Phenolic polymerization inhibitor, phenothiazine, nitroxide free radical and metal polymerization inhibitor are commonly used polymerization inhibitors in industry, but the polymerization inhibitors have a plurality of problems, on one hand, the polymerization inhibition effect is difficult to ensure, and especially in the high-temperature separation process, the single polymerization inhibitor is difficult to avoid the polymerization of products; on the other hand, rectification is a conventional means for removing the polymerization inhibitor, but most of the polymerization inhibitors have low saturated vapor pressure (especially high-efficiency polymerization inhibitors such as nitroxide free radicals), are difficult to separate in high-boiling products, and influence the use effect of the products.
In order to improve the polymerization inhibition effect, a plurality of composite polymerization inhibitors are developed in some patents. For example, patent CN1821207A discloses a composite polymerization inhibitor used for preventing monomer polymerization in the production process of methacrylic acid and its esters, which is prepared by compounding nitroxide free radical type compound and copper salt polymerization inhibitor, but the current composite polymerization inhibitors are all small molecules, and cannot solve the problem of difficult separation; in order to facilitate the removal of the catalyst, patent CN105820328A provides a method using a nitroxide radical polymer brush as a polymerization inhibitor. The nitroxide free radical polymer brush is a supported heterogeneous polymerization inhibitor; patent CN108855229A provides a preparation method and application of a supported catalytic/polymerization-inhibiting macroporous resin pellet, which takes methacrylic acid and styrene as monomers, obtains the macroporous resin pellet through monomer polymerization, and obtains the supported catalytic/polymerization-inhibiting macroporous resin pellet through esterification modification, polymerization inhibitor adding, sulfonation treatment and catalyst adding. The polymerization inhibitor and the product are in a solid-liquid two-phase state, so that the subsequent separation of the product and the polymerization inhibitor is convenient, and meanwhile, the polymerization inhibitor can only play a polymerization inhibition effect on a solid-liquid phase interface, so that the polymerization inhibition effect of the polymerization inhibitor is influenced to a certain extent.
In order to solve the problems, the patent CN109485745A provides a preparation method and application of a modified nitroxide radical polymerization inhibitor, the preparation method is characterized in that natural polysaccharide high-molecular sodium alginate is used as a main chain structure to prepare oil-soluble polysaccharide, and the nitroxide radical polymerization inhibitor is modified on the main chain of the oil-soluble polysaccharide through one-step esterification to finally obtain the modified nitroxide radical polymerization inhibitor.
Therefore, the need of developing a simple and effective method in the field is to solve the problems of poor polymerization inhibition effect, narrow application range, difficult removal and the like of the existing polymerization inhibitor.
Disclosure of Invention
The invention aims to provide a polymerization inhibitor which is a homogeneous phase load type composite polymerization inhibitor, and through the construction of the structure, the polymerization inhibition effect and the application range are improved, and the separation difficulty is reduced. The polymerization inhibitor solves the problem that the conventional polymerization inhibitor is easy to entrain while not influencing the polymerization inhibition effect, ensures the quality of the product, is suitable for a reaction system for preventing double-bond monomers from polymerizing, and is particularly suitable for a high-boiling point (methyl) acrylate reaction system.
In order to achieve the technical effects, the invention adopts the following technical scheme:
a polymerization inhibitor comprising a compound of the general structural formula:
A method for preparing the polymerization inhibitor comprises the following steps:
(1) preparation of Compounds of formula I from 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane (MHPD for short, CAS number: 6103-22-6) and benzyl trithiocarbonate propanoic acid (BSPA for short, CAS number: 497931-76-7)
(2) (meth) acrylic acid esters
With a compound of formula I to prepare a compound of formula II
Wherein R is1Is H or methyl, R2Is methyl or ethyl, m is 20 to 40, preferably 25 to 35;
(3) 4-hydroxy-2, 2,6, 6-tetramethylpiperidine-1-oxyl radical (4-hydroxy TEMPO for short)
And a compound of formula II to prepare a compound of formula III
(4) P-hydroxybenzoic acid
And reacting with a compound of formula III to prepare a polymerization inhibitor comprising a compound of the general structural formula:
and/or
Wherein R is1Is H or methyl, R2Is methyl or ethyl, m is 20 to 40, preferably 25 to 35, and 1. ltoreq. x. ltoreq.m.
Step (1) of the present invention is preferably carried out in the presence of a solvent including, but not limited to, dichloromethane, trichloromethane.
Step (1) of the present invention is preferably carried out in the presence of a catalyst comprising 4-dimethylaminopyridine and N, N-dicyclohexylcarbodiimide; wherein the molar ratio of 4-dimethylaminopyridine to MHPD is from 0.1 to 0.3:1, preferably from 0.15 to 0.25: 1; the molar ratio of N, N-dicyclohexylcarbodiimide to MHPD is from 1 to 3:1, preferably from 1.5 to 2.5: 1.
In step (1) of the present invention, the molar ratio of BSPA to MHPD is 1-3:1, preferably 1.5-2.5: 1.
The reaction temperature of the step (1) is 20-50 ℃, preferably 25-35 ℃, and the reaction time is 24-72 hours, preferably 48-60 hours.
After the step (1) reaction of the present invention is completed, the product can be isolated by a post-treatment method known in the art, and a preferred post-treatment method comprises the following steps: and after the reaction is finished, filtering the reaction solution, carrying out rotary evaporation and concentration, using diethyl ether for precipitation twice to obtain a light yellow solid, and carrying out vacuum drying to obtain the compound shown in the formula I.
Step (2) of the present invention is preferably carried out in the presence of a solvent including, but not limited to, N-dimethylformamide, N-dimethylacetamide.
Specific examples of the (meth) acrylate in the step (2) of the present invention include, but are not limited to, methyl methacrylate, methyl acrylate, ethyl methacrylate, and ethyl acrylate.
Step (2) of the present invention is carried out in the presence of an initiator, including but not limited to 2,2 '-azobisisobutyronitrile, 2' -azobisisoheptonitrile. The molar ratio of the initiator to the compound of formula I is from 0.4 to 0.6:1, preferably from 0.45 to 0.55:1, and the molar ratio of the initiator to the (meth) acrylate is from 0.01 to 0.03:1, preferably from 0.015 to 0.025: 1.
the reaction temperature of the step (2) is 70-100 ℃, preferably 80-90 ℃, and the reaction time is 8-24h, preferably 12-16 h.
After the step (2) reaction of the present invention is completed, the product can be isolated by a post-treatment method known in the art, and a preferred post-treatment method comprises the following steps: and after the reaction is finished, quickly cooling the reaction solution at low temperature, introducing air to stop the reaction, precipitating twice by using diethyl ether, and drying in vacuum to obtain the compound of the general formula II.
Step (3) of the present invention is preferably carried out in the presence of a catalyst which is a titanate-based catalyst, suitable examples including but not limited to tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropyl titanate, preferably tetrabutyl titanate and/or tetraisopropyl titanate. The molar ratio of catalyst to 4-hydroxy-TEMPO is from 0.1 to 1:1, preferably from 0.3 to 0.7: 1.
The mass ratio of 4-hydroxy TEMPO to the compound of formula II in step (3) according to the invention is 2-4:1, preferably 2.5-3.5: 1.
The reaction temperature of the step (3) of the invention is 100-150 ℃, preferably 110-130 ℃, and the reaction time is 1-6h, preferably 2-4 h.
In the step (4) of the present invention, the molar ratio of p-hydroxybenzoic acid to the compound of formula III is 2-3:1, preferably 2.3-2.7:1, the reaction temperature is 80-130 ℃, preferably 90-120 ℃, and the reaction time is 2-7h, preferably 3-6 h.
After the step (4) reaction of the present invention is completed, the product can be isolated by a post-treatment method known in the art, and a preferred post-treatment method comprises the following steps: and after the reaction is finished, cooling the reaction liquid, precipitating twice by using diethyl ether, and drying in vacuum to obtain the polymerization inhibitor.
The polymerization inhibitor is a high-molecular homogeneous phase load type polymerization inhibitor, is suitable for a reaction system for preventing double-bond monomers from polymerizing, and is particularly suitable for a high-boiling point (methyl) acrylate reaction system.
An acid alkene addition method comprising the steps of: in the presence of the polymerization inhibitor, the (meth) acrylic acid and the olefin undergo an acid-olefin addition reaction.
In the acid alkene addition method, the molar ratio of (methyl) acrylic acid to alkene is 1-10: 1, preferably 3-5: 1.
In the acid alkene addition method, the amount of the polymerization inhibitor is 1 to 5 weight percent based on the sum of the weight of (methyl) acrylic acid and alkene.
The acid alkene addition method has the reaction temperature of 30-120 ℃ and the absolute reaction pressure of 0.1-0.5 MPa.
In the acid alkene addition method, reaction liquid does not generate obvious oligomer, and good polymerization inhibition effect is shown. After the reaction is finished, the polymerization inhibitor is removed from the obtained reaction liquid through steps of reduced pressure rectification, scraper evaporation and the like, and the final product is obtained.
An esterification process comprising the steps of: in the presence of the polymerization inhibitor of the present invention, (meth) acrylic acid and a diol are subjected to an esterification reaction.
In the esterification method, the molar ratio of (methyl) acrylic acid to dihydric alcohol is 2-6: 1.
in the esterification process according to the invention, it is preferred to use water-carrying agents, such as toluene.
In the esterification process according to the invention, the amount of polymerization inhibitor used is 1% to 5% by weight, based on the sum of the weights of (meth) acrylic acid and glycol.
In the esterification process according to the invention, it is carried out in the presence of a catalyst in an amount of from 0.1% by weight to 2% by weight, based on the sum of the weights of (meth) acrylic acid and glycol.
In the esterification method, the reaction temperature is 100-150 ℃, and the reaction time is 1-5 h.
In the esterification method, reaction liquid does not generate obvious oligomer, and good polymerization inhibition effect is shown. After the reaction is finished, the polymerization inhibitor is removed from the obtained reaction liquid through steps of reduced pressure rectification, scraper evaporation and the like, and the final product is obtained.
A method of transesterification comprising the steps of: in the presence of the polymerization inhibitor of the present invention, methyl (meth) acrylate and alcohol are subjected to transesterification.
In the transesterification method of the present invention, the molar ratio of methyl (meth) acrylate to alcohol is 2 to 6: 1.
in the transesterification process according to the invention, the amount of polymerization inhibitor used is 1% to 5% by weight, based on the sum of the weights of methyl (meth) acrylate and alcohol.
In the ester exchange method, the reaction temperature is 140-160 ℃.
In the ester exchange method, the reaction solution does not generate obvious oligomer, and the good polymerization inhibition effect is shown. After the reaction is finished, the polymerization inhibitor is removed from the obtained reaction liquid through steps of reduced pressure rectification, scraper evaporation and the like, and the final product is obtained.
The invention has the positive effects that:
(1) the lipophilicity of the high molecular chain segment ensures that the polymerization inhibitor is in a homogeneous phase state in a reaction system, and the molecular chain segment has no active group, so that the system is suitable for the reaction system for preventing double-bond monomers from polymerizing, and is particularly suitable for a high-boiling point (methyl) acrylate reaction system;
(2) the introduction of the (methyl) acrylate monomer in the high-molecular chain segment can increase the modification density of the polymerization inhibitor, ensure the modification amount of the polymerization inhibitor and improve the polymerization inhibition efficiency of the load-type polymerization inhibitor per unit mass;
(3) the supported polymerization inhibitor is a composite polymerization inhibitor, and the polymerization inhibition effect of the system is further improved through the synergistic effect of the two polymerization inhibitors;
(4) the high-molecular homogeneous phase load type polymerization inhibitor has high molecular weight and high boiling point, can not be evaporated out by products, and ensures the color number and downstream use requirements of the products.
Detailed Description
The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the examples.
NMR spectrometer AVANCE III 400MHz, Bruker, Germany, TMS as reference.
Elemental analyzer, variao EL CUBE, Elementar analysisystem, germany, complete combustion.
Infrared FTS-6000, potassium bromide tabletting, scanning range 400 and 4000cm-1。
Gas chromatography, Shimadzu GC2010Plus, injection port temperature 280 ℃, FID temperature 300 ℃, septum purge (N)2) Flow rate 3.0mL/min, carrier gas (N)2) The flow rate is 1.0mL/min, and the split flow is injected, and the split flow ratio is 50: 1.
Colorimeter, Nessleiser, Hazen colorimetry, robiont instruments ltd.
GPC, polystyrene as standard reference.
Example 1
(1) Dissolving MHPD and benzyl trithiocarbonate propionic acid in dichloromethane, adding catalysts of 4-dimethylamino pyridine and N, N-dicyclohexyl carbodiimide, wherein the molar ratio of the benzyl trithiocarbonate propionic acid to the MHPD is 1:1, the molar ratio of the 4-dimethylamino pyridine to the MHPD is 0.1:1, the molar ratio of the N, N-dicyclohexyl carbodiimide to the MHPD is 1:1, reacting for 24 hours at 20 ℃, filtering after the reaction is finished, carrying out rotary evaporation concentration, precipitating twice by using solvent diethyl ether to obtain a light yellow solid, and carrying out vacuum drying to obtain a compound shown in a formula I;
infrared analysis of the compound of formula I obtained gave a 1732cm appearance-1Peak of ester bond of (1).
(2) Dissolving a compound shown in the formula I and methyl methacrylate in N, N-dimethylformamide, reacting under the initiation of 2, 2' -azobisisobutyronitrile, wherein the molar ratio of an initiator to the compound shown in the formula I is 0.4:1, the molar ratio of the initiator to the methyl methacrylate is 0.01:1, and reacting at 70 DEG CAfter 8 hours, quickly cooling at low temperature, introducing air to stop the reaction, precipitating with diethyl ether twice, and drying in vacuum to obtain a compound of a general formula II-1; infrared analysis of the resulting compound of formula II-1 at 1732cm-1The peak of ester bond is stronger than that of the compound in the formula I, and the weight average molecular weight of the product is 4432 by GPC analysis.
(3) Tetraethyl titanate is taken as a catalyst, the molar ratio of tetraethyl titanate to 4-hydroxy TEMPO is 0.1:1, the mass ratio of 4-hydroxy TEMPO to the compound of the formula II-1 is 2:1, and the compound of the general formula III-1 is prepared by reaction for 1h at the temperature of 100 ℃; the obtained compound of formula III-1 was subjected to elemental analysis, and a nitroxide compound was generated, indicating that the introduction of 4-hydroxy TEMPO was successful, and subjected to nuclear magnetic hydrogen spectroscopy, and a nuclear magnetic peak near 4.8ppm was derived from the methine hydrogen bonding an acetal and a benzene ring.
(4) Feeding materials according to the molar ratio of p-hydroxybenzoic acid to the compound of the general formula III-1 of 2:1, reacting for 2 hours at 80 ℃, cooling the reaction liquid after the reaction is finished, precipitating twice by using diethyl ether, and drying in vacuum to obtain the polymerization inhibitor of the general formula IV-1. When the obtained compound of the formula IV-1 was subjected to nuclear magnetic hydrogen spectroscopy, a nuclear magnetic peak at 8.3ppm was derived from the phenolic hydroxyl group, indicating that the introduction of hydroxybenzoic acid was successful, giving polymerization inhibitor 1, whose weight average molecular weight was 11231 by GPC analysis.
Preparing acrylic acid and camphene with a molar ratio of 10:1, wherein the addition amount of a polymerization inhibitor 1 is 2 wt%, feeding at a speed of 60 ℃, 0.1MPa and a volume space velocity of 5/h, and synthesizing the borneol acrylate by using a sulfonic acid resin bead A16 as a catalyst (Dow). The gas phase analysis of the reaction liquid shows that the total amount of the oligomer is 0.087 wt%, and the good polymerization inhibition effect is shown. And (3) performing two-stage reduced pressure rectification on the reaction liquid (the first stage, the pressure is 1.0-1.4 kPaA, the temperature is 50 ℃, the second stage, the temperature is 76-78 ℃, and the pressure is 0.3kPaA) to obtain a final product, wherein the final product does not contain a polymerization inhibitor, has the color number of 6, and meets the downstream use requirements.
Comparative example 1
4-hydroxy TEMPO and hydroquinone (mol ratio is 50: 1) are used as a composite polymerization inhibitor, acrylic acid and camphene with the mol ratio of 10:1 are prepared, the addition amount of the composite polymerization inhibitor is 2 wt%, feeding is carried out at the speed of 60 ℃, 0.1MPa and volume space velocity of 5/h, and sulfonic acid resin pellets A16 are used as a catalyst (Dow) to synthesize the borneol acrylate. The total amount of oligomers was 0.044 wt.% by gas-phase analysis of the reaction mixture. The polymerization inhibiting effect is good. And (3) performing two-stage reduced pressure rectification on the reaction liquid (the first stage is at the pressure of 1.0-1.4 kPaA, the temperature is 50 ℃, the second stage is at the temperature of 76-78 ℃, and the pressure is-0.3 kPaA) to obtain a final product, wherein the color number is 32, and the final product does not meet the downstream use requirements.
Example 2
(1) Dissolving MHPD and benzyl trithiocarbonate propionic acid in chloroform, adding catalysts 4-dimethylamino pyridine and N, N-dicyclohexyl carbodiimide, wherein the molar ratio of the benzyl trithiocarbonate propionic acid to the MHPD is 3:1, the molar ratio of the 4-dimethylamino pyridine to the MHPD is 0.3:1, the molar ratio of the N, N-dicyclohexyl carbodiimide to the MHPD is 3:1, reacting for 72 hours at 50 ℃, filtering after the reaction is finished, carrying out rotary evaporation concentration, precipitating twice by using solvent diethyl ether to obtain a light yellow solid, and carrying out vacuum drying to obtain a compound shown in the formula I;
infrared analysis of the compound of formula I obtained gave 1737cm-1Peak of ester bond of (1).
(2) Dissolving a compound shown in the formula I and methyl acrylate in N, N-dimethylacetamide, reacting under the initiation of 2, 2' -azobisisoheptonitrile, wherein the molar ratio of the initiator to the compound shown in the formula I is 0.6:1, the molar ratio of the initiator to the methyl acrylate is 0.03:1, reacting at 100 ℃ for 24 hours, rapidly cooling at low temperature, introducing air to stop the reaction, precipitating with diethyl ether twice, and vacuum-drying to obtain a compound shown in the general formula II-2; infrared analysis of the resulting compound of formula II-2 at 1737cm-1The peak of ester bond is stronger than that of the compound of formula I, and the weight average molecular weight of the product is 2242 by GPC analysis.
(3) Using tetrapropyl titanate as a catalyst, enabling the molar ratio of the tetrapropyl titanate to the 4-hydroxy TEMPO to be 1:1, enabling the mass ratio of the 4-hydroxy TEMPO to the compound of the formula II-2 to be 4:1, and reacting for 6 hours at 150 ℃ to obtain a compound of a general formula III-2; the obtained compound of formula III-2 was subjected to elemental analysis, and a nitroxide compound was generated, indicating that the introduction of 4-hydroxy TEMPO was successful, and subjected to nuclear magnetic hydrogen spectroscopy, and a nuclear magnetic peak near 4.7ppm was derived from the methine hydrogen bonding an acetal and a benzene ring.
(4) Feeding materials according to the molar ratio of p-hydroxybenzoic acid to the compound of the general formula III-2 of 3:1, reacting for 7 hours at 130 ℃, cooling the reaction liquid after the reaction is finished, precipitating twice by using diethyl ether, and drying in vacuum to obtain the polymerization inhibitor of the general formula IV-2. Upon nuclear magnetic hydrogen spectroscopy analysis of the obtained compound of the formula IV-2, a nuclear magnetic peak of 8.6ppm was derived from the phenolic hydroxyl group, indicating successful introduction of hydroxybenzoic acid, giving polymerization inhibitor 2, which has a weight average molecular weight of 5438 by GPC analysis.
Acrylic acid and butanediol in a molar ratio of 2:1 were added to the reaction kettle, toluene as a water-carrying agent was added, the amount of addition of polymerization inhibitor 2 was 1 wt%, and the amount of catalyst p-toluenesulfonic acid was 0.1 wt%, based on the amount of acrylic acid and butanediol. The reaction is carried out for 5 hours at the temperature of 100 ℃, and the obtained reaction liquid is analyzed by gas chromatography, the total amount of the oligomer is 0.101 wt%, and the good polymerization inhibition effect is shown. The reaction liquid is rectified by two stages of decompression (the first stage, the pressure is 0.8kPaA, the temperature is 120 ℃, the second stage, the temperature is 150 ℃, and the pressure is 0.5kPa) to obtain the final product, the color number is 8, no polymerization inhibitor is contained, and the downstream use requirements are met.
Comparative example 2
Polymerization inhibitor a was prepared in the same manner as in example 2 except that the mass ratio of 4-hydroxy TEMPO to the compound of formula II-2 was decreased from 4:1 to 0.1: 1.
Acrylic acid and butanediol in a molar ratio of 2:1 were added to the reaction vessel, toluene as a water-carrying agent was added, the amount of the added inhibitor a was 1 wt%, and the amount of the catalyst p-toluenesulfonic acid was 0.1 wt%, based on the amount of acrylic acid and butanediol. The reaction was carried out at 100 ℃ for 5 hours, and the obtained reaction solution had a solid, indicating that a part of the monomers was polymerized.
Example 3
(1) Dissolving MHPD and benzyl trithiocarbonate propionic acid in a solvent trichloromethane, adding a catalyst of 4-dimethylamino pyridine and N, N-dicyclohexyl carbodiimide, wherein the molar ratio of the benzyl trithiocarbonate propionic acid to the MHPD is 2:1, the molar ratio of the 4-dimethylamino pyridine to the MHPD is 0.2:1, the molar ratio of the N, N-dicyclohexyl carbodiimide to the MHPD is 2:1, reacting for 48 hours at 25 ℃, filtering after the reaction is finished, carrying out rotary evaporation concentration, precipitating twice with solvent diethyl ether to obtain a light yellow solid, and carrying out vacuum drying to obtain a compound shown in a formula I;
infrared analysis of the compound of formula I obtained gave a mass of 1725cm-1Peak of ester bond of (1).
(2) Dissolving a compound shown in the formula I and ethyl methacrylate in N, N-dimethylacetamide, reacting under the initiation of 2, 2' -azobisisobutyronitrile, wherein the molar ratio of an initiator to the compound shown in the formula I is 0.5:1, the molar ratio of the initiator to the ethyl methacrylate is 0.02:1, reacting at 80 ℃ for 12 hours, rapidly cooling at low temperature, introducing air to stop the reaction, precipitating with diethyl ether twice, and vacuum-drying to obtain a compound shown in the general formula II-3; the resulting compound of formula II-3 was analyzed by infrared at 1725cm-1The peak of ester bond is stronger than that of the compound in the formula I, and the weight average molecular weight of the product is 3292 by GPC analysis.
(3) Tetrabutyl titanate is used as a catalyst, the molar ratio of tetrabutyl titanate to 4-hydroxy TEMPO is 0.3:1, the mass ratio of 4-hydroxy TEMPO to the compound of the formula II-3 is 2.5:1, and the compound of the general formula III-3 is prepared after reaction for 2h at the temperature of 110 ℃; the obtained compound of formula III-3 was subjected to elemental analysis, and a nitroxide compound was generated, indicating that the introduction of 4-hydroxy TEMPO was successful, and subjected to nuclear magnetic hydrogen spectroscopy, and a nuclear magnetic peak near 4.8ppm was derived from the methine hydrogen bonding an acetal and a benzene ring.
(4) Feeding materials according to the molar ratio of p-hydroxybenzoic acid to the compound of the general formula III-3 of 2.3:1, reacting for 3 hours at 90 ℃, cooling the reaction liquid after the reaction is finished, precipitating twice by using diethyl ether, and drying in vacuum to obtain the polymerization inhibitor of the general formula IV-3. When the obtained compound of the formula IV-3 was subjected to nuclear magnetic hydrogen spectroscopy, a nuclear magnetic peak of 7.5ppm was derived from the phenolic hydroxyl group, indicating that the introduction of hydroxybenzoic acid was successful, giving polymerization inhibitor 3, whose weight average molecular weight was 7032 by GPC analysis.
Methyl methacrylate and butanol were added to the reaction kettle in a molar ratio of 2:1, and the amount of polymerization inhibitor 3 added was 3 wt% based on the amount of methyl methacrylate and butanol used. Heating and raising the temperature, and after the reflux of the top of the rectifying tower is stable and the temperature is stable at 62-64 ℃, performing distillation according to a reflux ratio of 1:1, in the reaction process, the temperature of the reaction liquid is controlled to ensure that the extraction amount and the extraction temperature at the top of the tower are stable, and the reaction is stopped when the temperature of the kettle rises to 150 ℃ and the temperature at the top of the tower obviously rises. The obtained reaction solution was analyzed by gas chromatography, and the total amount of the oligomer was 0.055 wt%, which showed a good effect of inhibiting polymerization. And (3) performing two-stage reduced pressure rectification on the reaction liquid (the first stage, the pressure of 10kPaA, the temperature of 100 ℃, the second stage, the temperature of 9 ℃ and the pressure of 2kPa) to obtain a final product, wherein the color number is 3, no polymerization inhibitor is contained, and the downstream use requirement is met.
Example 4
(1) Dissolving MHPD and benzyl trithiocarbonate propionic acid in solvent dichloromethane, adding catalyst 4-dimethylamino pyridine and N, N-dicyclohexyl carbodiimide, wherein the molar ratio of the benzyl trithiocarbonate propionic acid to the MHPD is 2:1, the molar ratio of the 4-dimethylamino pyridine to the MHPD is 0.2:1, and the molar ratio of the N, N-dicyclohexyl carbodiimide is 0.2:1The mol ratio of imine to MHPD is 2:1, the reaction is carried out for 60 hours at the temperature of 35 ℃, after the reaction is finished, the filtration is carried out, the rotary evaporation and the concentration are carried out, the solvent ether is precipitated for two times, light yellow solid is obtained, and the compound of the formula I is obtained after vacuum drying;
infrared analysis of the compound of formula I obtained gave a profile of 1719cm-1Peak of ester bond of (1).
(2) Dissolving a compound shown in the formula I and ethyl acrylate in N, N-dimethylacetamide, reacting under the initiation of 2, 2' -azobisisoheptonitrile, wherein the molar ratio of the initiator to the compound shown in the formula I is 0.5:1, the molar ratio of the initiator to the ethyl acrylate is 0.02:1, reacting at 90 ℃ for 16 hours, rapidly cooling at low temperature, introducing air to stop the reaction, precipitating with diethyl ether twice, and vacuum-drying to obtain a compound shown in the general formula II-4; the resulting compound of formula II-4 was analyzed by infrared analysis at 1719cm-1The peak of ester bond is stronger than that of the compound in the formula I, and the weight average molecular weight of the product is 3012 by GPC analysis.
(3) Reacting for 2h at 110 ℃ by using tetraisopropyl titanate as a catalyst and the molar ratio of tetraisopropyl titanate to 4-hydroxy TEMPO being 0.3:1, the mass ratio of 4-hydroxy TEMPO to the compound of formula II-4 being 3.5:1 to prepare the compound of the general formula III-4; the obtained compound of formula III-4 was subjected to elemental analysis, and a nitroxide compound was generated, indicating that the introduction of 4-hydroxy TEMPO was successful, and subjected to nuclear magnetic hydrogen spectroscopy, and a nuclear magnetic peak near 4.9ppm was derived from the methine hydrogen bonding an acetal and a benzene ring.
(4) Feeding materials according to the molar ratio of p-hydroxybenzoic acid to the compound of the general formula III-4 of 2.7:1, reacting for 6h at 120 ℃, cooling the reaction liquid after the reaction is finished, precipitating twice by using diethyl ether, and drying in vacuum to obtain the polymerization inhibitor of the general formula IV-4. On the obtained compound of the formula IV-4, nuclear magnetic hydrogen spectrum analysis was performed, and a nuclear magnetic peak of 7.9ppm was derived from the phenolic hydroxyl group, indicating that introduction of hydroxybenzoic acid was successful, to obtain polymerization inhibitor 4, whose weight average molecular weight was 6763 by GPC analysis.
Methacrylic acid and cyclohexene with a molar ratio of 2:1 are prepared, the addition amount of a polymerization inhibitor 4 is 3 wt%, feeding is carried out at the speed of 110 ℃, 0.1MPa and the volume space velocity of 0.2/h, and sulfonic acid resin pellets A16 are used as a catalyst (Dow) to synthesize cyclohexyl methacrylate. The gas phase analysis of the reaction liquid shows that the total amount of the oligomer is 0.093 wt%, and the good polymerization inhibition effect is shown. And (3) performing two-stage reduced pressure rectification on the reaction liquid (the first stage, the pressure of 3kPaA, the temperature of 80 ℃, the second stage, the temperature of 90 ℃ and the pressure of 1kPa) to obtain a final product, wherein the color number is 8, no polymerization inhibitor is contained, and the downstream use requirement is met.
Comparative example 3
After the reaction of the reaction solution of the compound of the general formula III-4 is finished, cooling the reaction solution, precipitating twice by using diethyl ether, and vacuum drying to obtain the compound of the general formula III-4, preparing methacrylic acid and cyclohexene with a molar ratio of 2:1, wherein the addition amount of the compound of the general formula III-4 is 3 wt%, feeding at 110 ℃, 0.1MPa and a volume space velocity of 0.2/h, and synthesizing cyclohexyl methacrylate by using a sulfonic acid resin bead A16 as a catalyst (Dow). Gas phase analysis of the reaction solution revealed that the reaction solution had solids, indicating that a portion of the monomer was polymerized.
Claims (18)
1. A polymerization inhibitor comprising a compound of the general structural formula:
Wherein R is1Is H or methyl, R2Is methyl or ethyl, m is 20-40, and x is not less than 1 and not more than m.
2. The polymerization inhibitor according to claim 1, wherein m is 25 to 35.
3. A method for preparing the polymerization inhibitor according to claim 1, comprising the steps of:
(1) preparation of 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane and benzyl trithiocarbonate propanoic acid
(2) (meth) acrylic acid esters
With a compound of formula I to prepare a compound of formula II
Wherein R is1Is H or methyl, R2Is methyl or ethyl, m is 20-40;
(3) 4-hydroxy-2, 2,6, 6-tetramethylpiperidine-1-oxyl radical
And a compound of formula II to prepare a compound of formula III
(4) P-hydroxybenzoic acid
And reacting with a compound shown in a formula III to prepare the polymerization inhibitor.
4. The method of claim 3, wherein m is 25-35.
5. The process of claim 3, wherein step (1), is carried out in the presence of a catalyst comprising 4-dimethylaminopyridine and N, N-dicyclohexylcarbodiimide; wherein the molar ratio of the 4-dimethylamino pyridine to the 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is 0.1-0.3: 1; the molar ratio of the N, N-dicyclohexylcarbodiimide to the 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is 1-3: 1.
6. The process of claim 5, wherein the molar ratio of 4-dimethylaminopyridine to 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is from 0.15 to 0.25: 1; the molar ratio of the N, N-dicyclohexylcarbodiimide to the 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is 1.5-2.5: 1.
7. The method according to claim 3, wherein in the step (1), the molar ratio of the benzyltrithiocarbonate-based propionic acid to the 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is 1-3: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (1) is 20-50 ℃, and the reaction time is 24-72 h.
8. The method according to claim 7, wherein in the step (1), the molar ratio of the benzyltrithiocarbonate-based propionic acid to the 5-methyl-5-hydroxymethyl-2-phenyl-1, 3-dioxane is 1.5-2.5: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (1) is 25-35 ℃, and the reaction time is 48-60 h.
9. The method according to claim 3, wherein the (meth) acrylate in step (2) comprises one or more of methyl methacrylate, methyl acrylate, ethyl methacrylate, and ethyl acrylate.
10. The process of claim 3, wherein step (2) is carried out in the presence of an initiator comprising 2,2 '-azobisisobutyronitrile and/or 2, 2' -azobisisoheptonitrile, at a molar ratio of the initiator to the compound of formula I of 0.4-0.6:1, and at a molar ratio of the initiator to the (meth) acrylate of 0.01-0.03: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (2) is 70-100 ℃, and the reaction time is 8-24 h.
11. The process of claim 10, wherein the molar ratio of the initiator to the compound of formula I is from 0.45 to 0.55:1, and the molar ratio of the initiator to the (meth) acrylate is from 0.015 to 0.025: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (2) is 80-90 ℃, and the reaction time is 12-16 h.
12. The method of claim 3, wherein step (3) is performed in the presence of a catalyst comprising one or more of tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraisopropyl titanate; the molar ratio of catalyst to 4-hydroxy-TEMPO is 0.1-1: 1.
13. The process of claim 12, wherein the molar ratio of catalyst to 4-hydroxy-TEMPO is 0.3-0.7: 1.
14. The method according to claim 3, wherein the mass ratio of 4-hydroxy TEMPO to the compound of formula II in step (3) is 2-4: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (3) is 100-150 ℃, and the reaction time is 1-6 h.
15. The method of claim 14, wherein the mass ratio of 4-hydroxy TEMPO to the compound of formula II in step (3) is 2.5-3.5: 1; and/or the presence of a gas in the gas,
the reaction temperature of the step (3) is 110-130 ℃, and the reaction time is 2-4 h.
16. The method according to claim 3, wherein in the step (4), the molar ratio of p-hydroxybenzoic acid to the compound of formula III is 2-3:1, the reaction temperature is 80-130 ℃, and the reaction time is 2-7 h.
17. The method of claim 16, wherein in the step (4), the molar ratio of p-hydroxybenzoic acid to the compound of formula III is 2.3-2.7:1, the reaction temperature is 90-120 ℃, and the reaction time is 3-6 h.
18. Use of a polymerization inhibitor according to claim 1 or 2 or a polymerization inhibitor prepared by the process according to any one of claims 3 to 17 as polymerization inhibitor in a reaction selected from the group consisting of: an acid-olefin addition reaction of (meth) acrylic acid and an olefin, an esterification reaction of (meth) acrylic acid and a diol, or a transesterification reaction of methyl (meth) acrylate and an alcohol.
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